Young men who have sex with men (YMSM) are profoundly impacted by HIV/AIDS in the United States, but relatively little research has evaluated HIV risk in this population. Notably, binge drinking and illicit drug use have been found to consistently predict sexual risk behavior in YMSM, but few studies have focused on developing interventions for substance-using YMSM. Behavioral diaries are widely-used as a survey method for observing change in health-related behaviors, and behavioral self-monitoring strategies are also frequently used in clinical interventions to induce health-behavior change. Social cognitive processes such as motivation influence the success of self-monitoring, and our previous research found that MSM with greater HIV risk reduction motivation were more likely to reduce their reported unprotected sex over the course of a sexual diary study. However, it is unclear whether motivated MSM simply reduced their sexual risk behavior on their own, or whether they actually benefited from self-monitoring. Despite recent calls to examine the utility of self- monitoring and diary approaches to change sexual risk behavior in YMSM specifically, several important questions remain unanswered: 1) When do sexual diary studies become self-monitoring interventions?; and 2) For whom do self-monitoring diaries serve as interventions? The overarching goal of this study is to examine the conditions under which sexual diaries become self-monitoring interventions for binge-drinking and drug- using YMSM in order to maximize their value as a tool for observation and intervention. To achieve this goal, we will examine the following specific aims: Aim 1: Describe which YMSM, under which situational and contextual conditions, show change in reported sexual risk behavior using web-based behavioral diaries; Aim 2: Experimentally compare frequencies of behavioral diary administration on change in reported sexual risk behavior and participant attrition; and Aim 3: Test the effect of delivering individualized risk behavior feedback. The proposed study will recruit 360 binge-drinking and/or drug-using YMSM (ages 16-29) online into a 2-month web-based sexual diary study. In accordance with Aim 1, we will examine group differences in change in reported sexual risk behavior by age cohort (adolescents, emerging adults, young adults), as well as the influence of social cognitive variables (HIV risk reduction motivation, intentions, and self-efficacy) and substance use (alcohol and illicit drug use) on sexual risk behavior. To achieve Aim 2, we will evaluate differences in reported behavior change and participant attrition by frequency of behavioral diary administration (daily diaries, weekly diarie, or no diaries). For Aim 3, we will test the effect of providing individualized risk behavior feedbak by randomizing YMSM into feedback or no feedback groups. Risk behavior feedback will illustrate: frequency of sexual risk behavior, substance use, and the correlation between these variables. The data collected in this study will aid the PI in transitioning to intervention development research and support a larger grant application to develop a self-monitoring intervention for substance-using YMSM.